The present invention relates to methods and apparatuses for measuring velocities pertaining to the flow of fluids, more particularly to probe-like devices used in association with anemometers for measuring such velocities.
The x and y components of velocity of two-dimensional fluid flow are known to be measurable using a hot-wire anemometer in combination with a cross-wire (or x-wire) probe. Two-wire probes such as x-wire probes represent a genre of hot-wire probes. X-wire probes comprise prongs which support two sensor wires such that the two wires are perpendicular to each other in the measurement plane of interest and are separated by a small distance in the out-of-plane direction.
Most frequently, velocity measurements are made so that the prongs are oriented in the primary fluid flow direction, so as to not interfere with fluid flow over the wires; a probe used in this manner is referred to as an xe2x80x9cin-linexe2x80x9d probe. The prongs may also be oriented perpendicular to the plane of interest; a probe used in this manner is referred to as a xe2x80x9ccross-flowxe2x80x9d probe.
Probes with varying designs are commercially available. Some probes are xe2x80x9cstraightxe2x80x9d probes, having prongs that are oriented along the axis of the probe body; these may be used as either in-line probes or cross-flow probes. Also available are so-called xe2x80x9cboundary layerxe2x80x9d probes, wherein the prongs of an in-line probe are curved approximately ninety degrees (90xc2x0) so that measurements of flow along a boundary (e.g., a wall) may be made very close to the boundary.
None of these conventional probe designs is adequate for making velocity measurements in a wall aperture.
A conventional straight probe oriented in the in-line direction can be used for making velocity measurements in an aperture only if the aperture is longer than the probe and its support; even under such circumstances, such an in-line probe will be incapable of making measurements closer to the downstream edge than the length of the probe and its support.
A conventional straight probe oriented in the cross-flow direction is ordinarily impractical for making velocity measurements in an aperture, because the prongs will interfere with fluid flow over the probe, rendering the measurements highly inaccurate. Such a cross-flow probe will be useful for such purposes only if the cross-stream dimension of the aperture is greater than length of the probe and its support.
A boundary layer probe also proves unsatisfactory for purposes of making velocity measurements in an aperture. A boundary layer probe does not require a large cross-stream dimension; however, a boundary layer probe is limited, insofar as how close it can get to the downstream edge, by interference of the prongs with the downstream edge. In many applications, the boundary layer probe cannot achieve sufficient closeness.
Accordingly, commercially available probes are not practical for measuring x and y velocity components very close to the downstream edge of an aperture. This deficiency is especially manifest when it is desirable to make measurements in an entire aperture, including the aperture region which is close to the downstream edge.
Among the many applications of hot-wire probes are those involving measurement of vorticity, which requires measurements of velocity at more than one location. Hot-wire probes have been used to simultaneously measure the velocity vector at several locations; however, the hot-wire probes known for measuring vorticity typically require at least six wires, and thus are rather complex.
In view of the foregoing, it is an object of the present invention to provide method and apparatus for making fluid velocity measurements in an aperture.
It is another object of the present invention to provide method and apparatus for making fluid velocity measurements in a region of an aperture which is proximate the downstream edge of the aperture.
It is a further object of the present invention to provide method and apparatus for making fluid velocity measurements in an entire aperture.
Another object of the present invention is to provide method and apparatus for measuring fluid vorticity using relatively uncomplicated probe instrumentation.
In accordance with many embodiments of the present invention, a fluid velocity measurement device comprises an approximately linear member, a set of nonlinear prongs and an x-wire combination. The member is approximately characterized by a member axis. The member has a member axial extremity. The prongs protrude from the member at the member axial extremity. The prongs have corresponding prong tips distanced from the member axial extremity. The x-wire combination communicates with the prong tips. The device approximately defines a device plane passing through the device. The x-wire combination approximately defines an x-wire plane passing through the x-wire combination. The x-wire plane and the member axis are approximately parallel to each other. The x-wire plane and the device plane are approximately perpendicular to each other.
The present invention typically features a novel combination of indicia of both a boundary layer probe and a cross-flow probe. The inventive probe is similar to a boundary layer probe insofar as the prongs are curved approximately ninety degrees (90xc2x0) from the probe (and probe support). However, according to a conventional boundary layer probe, the wires are disposed in a manner which furthers utilization of the probe as an in-line probe. In contrast, the present invention uniquely disposes the wires in a manner which furthers utilization of the probe as a cross-flow probe.
The present invention was motivated by the problem of how to measure x and y velocity components close to the downstream edge of an aperture. The present invention advantageously allows velocity measurements to be made in the entire aperture, including the region close to the downstream edge. When the inventor originally consulted several individuals with expertise in hot-wire measurements, it became apparent that commercially available probes were unsatisfactory for purposes of effecting velocity measurements proximate the downstream edge of an aperture.
The suggestions offered by the experts all involved using cross-flow or in-line probes supported with structures inside the wall aperture. In accordance with the inventor""s existing experimental set-up, all previous measurements had been made by the inventor with the probe supported and positioned using an external traverse system. The experts"" suggestions would have been difficult to implement in the context of the inventor""s existing experimental setup, and in any case would not have allowed measurements over the full range of out-of-plane positions. In contrast, the probe device according to this invention not only lends itself to being situated external to the aperture, but also is capable of effecting velocity measurements over the full range of out-of-plane positions, thereby at least substantially covering the entire aperture.
Accordingly, the present invention advantageously permits x-wire measurements of fluid velocity at all locations inside a wall aperture, including the region very close to the downstream edge. Further advantageously, the inventive probe may be supported externally of the wall, and may be freely and quickly moved to any position inside or outside of the aperture, and without having to make any setup changes.
The above-noted concurrently filed application entitled xe2x80x9cMethod for Measuring Vorticityxe2x80x9d discloses an inventive methodology for effecting vorticity measurements. The x-wire probe according to this invention lends itself to efficacious use in association with the inventive vorticity measurement methodology. With regard to the measurement of vorticity, an advantage of using the inventive x-wire probe disclosed herein derives from its relative simplicity as compared with the more complex hot-wire probes which have been known for measuring vorticity. It is emphasized, however, that the present invention admits of practice for measuring fluid velocity in multifarious applications, including those related to vorticity and those unrelated to vorticity.
Other objects, advantages and features of this invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.
Hereby incorporated herein by reference is the following 180-page U.S. Navy technical report which discloses various aspects of the present invention: Paul J. Zoccola. Jr., xe2x80x9cExperimental Investigation of Flow-Induced Cavity Resonance,xe2x80x9d NSWCCD-TR-2000/010, June 2000, Signatures Directorate Technical Report, Naval Surface Warfare Center, Carderock Division, West Bethesda, Md., 20817-5700. The substance of this report is also available under reference number 9969545 from Bell and Howell Company, Skokie, Ill. in the form of the inventor""s doctoral dissertation. This dissertation is also expected to be available from the library of the Catholic University of America, Washington, D.C.